A new method of preparing superabsorbent PVF porous foam through the simultaneous acidification of water glass solution–aspect of environmental protection

Abstract

To reduce the wastewater pollution problem, silica particles that have resulted from simultaneous sulfuric acidification of water glass solution serve as the pore-forming agent for preparing superabsorbent PVF/SiO 2 foam in this study. This is a departure from the traditional porous PVF/starch foam's manufacture method. The pore structure of PVF/SiO 2 foam is very different from that of PVF/starch foam. The effect of the concentration of these pore-forming agents on the pore structure, mechanical modulus, and water adsorption capacity of PVF/starch and PVF/SiO 2 foams are investigated in this study. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39894.

A novel method of making PVF porous foam without using the pore forming agent

“…Also, this SD phenomenon can be accelerated by the decreased viscosity of the PVA reaction solution when the reaction temperature is increased from 50°C to 60°C. Since the viscosity of the PVA reaction solution adopted in the present experiments increases with the increase of either PVA concentration or the decrease of solution temperature, as illustrated by the schematic diagram in Figure , because of its decreased viscosity, the drainage velocity of the PVF polymer formatted at 60°C between two water bubbles is faster than that of 50°C under the same PVA concentration. This increased drainage velocity reduces the wall thickness of PVF formatted between two water bubbles, and therefore can easily induce a larger pore size in PVF foams at 60°C than that at 50°C.…”

“…The water adsorption capacity and the water desorption rate of PVF foams were determined using DuPont TGA‐Q50 thermal analyzer . Under nitrogen flow rate of 100 cm 3 /min, the water adsorption capacity of PVF foams were calculated from the weight loss at 100°C when each 20 mg sample was heated from room temperature to 600°C with a heating rate of 10°C/min, and the water desorption rate was determined when each sample was heated at 50°C for 50 minutes, respectively …”

“…All these results coincide with the SEM observations of Figures (a–e) and (a–e): a higher porosity but smaller pore size foam can be obtained when the reaction temperature is decreased from 60°C to 50°C under the same PVA concentration. Interestingly, as can be observed in those SEM pictures, many micron voids exist on the pore walls of PVF foams made by either 12 and 13 wt % PVA (which are identical to those PVF pore walls when SiO 2 particles served as the pore‐forming agent in our previous work), but they disappear on the pore walls of those PVF foams made by 14–16 wt % PVA.…”

“…As the additional acetalization continues, the nematic domains continue to nucleate and the small water bubbles start to separate from the PVF nucleates. Those micron voids that exist on the pore walls of PVF foams made by 12 and 13 wt % PVA [see Figures (a, b) and (a, b)] are believed to be formed by condensed water at this stage . At the second stage of the reaction, as shown by Figure (b) after reaction of 15 minutes (i.e., when the conversion rate of formaldehyde achieves 20%; see Figure ), since the large free energy barrier between small water bubbles is already overcome, we observe fast movement of small condensed water molecules followed by rapid coalescence with large water bubbles contained in the original PVA solution, and the drainage of PVF polymers between two water bubbles.…”

“…However, when those starch pore‐forming agents were washed by water in the final step involved in manufacturing PVF foam, the high concentration of starch in the wastewater always caused serious environmental pollution problems because of its high COD value. In our previous article, we reported our efforts to reduce these high COD values by preparing PVF porous foam through the simultaneous acidification of water glass solution to produce silica particles as the pore‐forming agent when PVF foam was made . However, even with the benefits of low cost and low environmental impact, mixing those silica particles homogeneously with the PVA solution always proved difficult during the fabrication processes, due to the increased viscosity caused by the increased concentration of water glass solution.…”